1. Field of the Invention
The present invention relates to an exposure apparatus.
2. Description of the Related Art
A scanning exposure apparatus is conventionally known which exposes a pattern of an original (such as a mask and a reticle) onto a substrate via a projection optical system by utilizing light from a light source and by scanning the original and the substrate. The substrate has a plurality of shots (each shot being an area to be exposed by one exposure action); when the pattern of the original is transferred onto one shot, an exposure area is stepped to another shot by a substrate stage. By repeating the exposing and stepping, the original's pattern is exposed onto all shots on the substrate.
A throughput is an important parameter in the exposure, and the exposure sequence among shots affects the throughput. Japanese Patent Laid-Open No. (“JP”) 04-037114 determines the exposure sequence among shots so as to minimize moving distances of the substrate stage in a scanning direction (such as a Y direction) and in a non-scanning or sub-scanning direction (such as an X direction) orthogonal to the optical-axis direction (such as a Z direction) and the scanning direction. JP 04-037114 attempts to improve the throughput by minimizing the moving amount of the substrate stage or the driving time period.
The exposure apparatus corrects a curvature of field (“COF”) of an exposure area by driving a COF correcting lens in a projection optical system for focus correction. However, the driving responsibility of the COF correcting lens is lower than that of the substrate stage; even when the substrate stage moves to an exposure area to a target shot, the COF correcting lens does not reach the target position and the exposure may not immediately be ready to start. In addition, for a highly precise alignment, a rotation correction around the Z axis for each shot is more important than a rotational correction around the Z axis for the overall substrate. The responsibility of the rotational driving of the substrate stage around the Z axis is lower than that of the driving in the X or Y direction. From the above, a method described in JP 04-037114 cannot necessarily improve the throughput.